Variable compression ratio(VCR) engine

Abstract

The present invention relates to a variable compression ratio (VCR) engine and a method for driving the variable compression ratio (VCR) engine. The variable compression ratio (VCR) engine (1) comprises at least one cylinder (2), and a piston (3) configured to perform a predetermined piston stroke within the cylinder (2) is movably disposed within the cylinder (2). The engine also comprises a setting unit (4) for setting a predetermined compression ratio by setting a predetermined clearance position (11). The VCR engine (1) further comprises a control unit (5) for setting at least one temporary clearance position (15) different from the predetermined clearance position (11) and for inducing at least one piston movement having the temporary clearance position (15).

Description

Technology Field

[0001] The present invention relates to a variable compression ratio (VCR) engine and a method for driving a variable compression ratio (VCR) engine. Background Technology

[0002] In reciprocating piston combustion engines, the compression ratio is an important parameter for combustion, thermal efficiency, and exhaust gas emissions.

[0003] The compression ratio of a combustion engine represents the ratio of the combustion chamber volume from the maximum capacity to the minimum capacity. In a piston engine, the compression ratio is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke and the volume of the combustion chamber when the piston is at the top of its stroke. Thus, the compression ratio can be calculated as the ratio between the sum of the displacement volume and the clearance volume and the clearance volume. The displacement volume is the volume within the cylinder that the piston displaces from the beginning of the compression stroke to the end of the compression stroke. The clearance volume is the volume of the space within the cylinder remaining at the end of the compression stroke.

[0004] Compression ratio is generally selected to achieve the best engine performance. Often, high-load engine performance is the most relevant factor in the selection. For optimal performance across the entire operating range, a variable compression ratio is desirable.

[0005] Different methods for changing the compression ratio in smaller reciprocating piston combustion engines are known, for example, eccentric sleeves around piston pins or main bearings, or mechanisms for adjusting the distance between an eccentric shaft and the cylinder head and crankshaft centerline are known.

[0006] The compression ratio can be changed by allowing gas to enter an additional volume outside the cylinder, as disclosed in EP2677141 A1, for example, or by a displaceable outlet valve seat, as disclosed in JPS61-197731 A.

[0007] A large reciprocating piston combustion engine typically comprises one or more cylinders equipped with cylinder liners, one or more pistons movably disposed within each cylinder liner, and a crankshaft rotatably disposed within a crankshaft housing, wherein each piston is connected to each crosshead via a piston rod, and each crosshead is connected to the crankshaft via a connecting rod to drive the crankshaft. The piston rod is generally guided linearly along its longitudinal axis, and each crosshead converts the linear motion of the piston rod into the non-linear motion of the connecting rod.

[0008] EP2687707 A2 discloses a large reciprocating piston combustion engine in which a control device for controlling the compression ratio of the reciprocating piston combustion engine is provided on the crosshead and / or piston. For example, the piston rod may be extended by a hydraulic cylinder located at the crosshead pin. Thus, the possible maximum and minimum positions of the piston are changed.

[0009] In combustion engines, carbon can accumulate above the piston's top dead center position during prolonged operation, and wear steps may also occur.

[0010] When the compression ratio is constant, this is not a problem because the piston will never reach this range.

[0011] However, when changing the compression ratio by determining the maximum and minimum positions of the piston within the cylinder, different maximum piston positions of the piston, particularly the normal piston ring, can be obtained.

[0012] If the engine has operated at a "low" compression ratio with a relatively large margin for a long time and then the compression ratio suddenly increases, the piston rings will pass through areas of wear steps and carbonized deposits.

[0013] Therefore, reliable piston running performance is not guaranteed, and damage to the piston, piston rings, and cylinder liners may occur. For reliable engine operation in Variable Compression Ratio (VCR) engines, it is essential to manage carbon buildup and avoid wear discrepancies. The problem to be solved

[0014] The objective of the present invention is to provide a variable compression ratio (VCR) engine and a method of operating the variable compression ratio (VCR) engine that avoid the disadvantages of the prior art, and in particular have more continuous performance and require less maintenance than the engine of the prior art. means of solving the problem

[0015] The above objective is achieved by a variable compression ratio (VCR) engine and a method of operating the variable compression ratio (VCR) engine according to an independent claim.

[0016] The above objective is achieved by a variable compression ratio (VCR) engine comprising at least one cylinder, wherein a piston configured to perform a predetermined piston stroke within the cylinder is arranged to move within the cylinder. The variable compression ratio (VCR) engine includes a setting unit for setting a predetermined compression ratio by setting a predetermined clearance position.

[0017] The piston moves between the bottom dead center and the top dead center. The distance between the bottom dead center and the top dead center corresponds to the piston displacement length, which can be determined by the length of the crankshaft and the length of the connecting rod.

[0018] At top dead center, the piston is in a clearance position.

[0019] The preset clearance position is the preset normal position of the piston, specifically the normal position of the normal ring, and corresponds to the respective clearance volume.

[0020] The normal ring is a seal ring located in the uppermost groove of the piston.

[0021] In most cases, since the displacement length and displacement volume cannot change for a given piston / cylinder unit during operation due to the fixed lengths of the cylinder diameter, piston, piston rod, connecting rod, and crankshaft, the setting of the clearance volume defines the compression ratio.

[0022] Generally, there is the highest possible normal position within the cylinder that the piston can reach, and this normal position corresponds to the minimum possible clearance volume and the maximum possible compression ratio.

[0023] To select a smaller compression ratio, the range of motion of the piston within the cylinder can be varied to obtain a lower clearance position, a larger clearance volume, and thus a smaller compression ratio.

[0024] According to the present invention, the VCR-engine further includes a control unit for setting at least one temporary clearance position different from the preset clearance position and for inducing at least one piston movement having the temporary clearance position.

[0025] Preferably, the temporary clearance position is above the preset clearance position; in other words, it is closer to the highest possible normal position as the preset clearance.

[0026] Preferably, the control unit is configured to subsequently set a preset clearance position and also induce piston movement having the preset clearance position.

[0027] Piston motion with a temporary clearance position is motion between the bottom position and the normal position, and the normal position corresponds to the temporary clearance position.

[0028] Preferably, the absolute maximum position of the piston and thus the temporary clearance position corresponding to the minimum clearance volume and the maximum possible compression ratio are selected.

[0029] If a temporary clearance position corresponding to a smaller clearance volume is occasionally obtained compared to a preset clearance position, carbon accumulation can be reduced. The piston cleans the inner wall of the cylinder while moving along it. Deposits of carbon material that may accumulate on the inner wall of the cylinder in the region above the piston's clearance position can be removed as the piston, particularly the normal ring, passes through that region.

[0030] Preferably, the control unit is configured to induce at least one piston movement having a temporary spare position according to at least one predetermined plan.

[0031] The plan preferably specifies consecutive values ​​of temporary clearance positions, time intervals or the number of administrations and / or setting cycles for maintaining temporary clearance positions.

[0032] The plan may include a repetitive setting of piston motion having a temporary clearance position corresponding to a smaller clearance volume compared to a preset clearance position after a predetermined time interval or after a predetermined piston stroke motion.

[0033] The plan can provide a curve that defines the clearance position over time or according to the number of piston strokes. The temporary clearance position varies along this curve over time or according to the number of piston strokes. The plan can define a stepwise change in the temporary clearance position.

[0034] If the clearance position changes too quickly or with too large a change in distance, there is a risk that the piston will pass through an area containing wear steps, which must be prevented. By appropriately changing the clearance position, the piston approaches the area where deposits may be present slowly. The piston can remove more deposits over the entire change curve.

[0035] In addition, removing the deposit may take some time. Therefore, the plan can specify the time during which a temporary margin is maintained or the number of piston strokes.

[0036] In an advantageous embodiment of the VCR-engine, the control unit is configured to induce piston movement having a temporary spare position when necessary.

[0037] Alternatively or additionally, the control unit is configured to induce at least one piston movement having a temporary clearance position every 100 to 500,000 piston strokes.

[0038] Alternatively or additionally, the control unit is configured to induce at least one piston movement having a temporary spare position every 1 hour to 2 months of operation time.

[0039] The VCR engine comprises at least two cylinders, and the control unit is configured to induce a piston movement having a temporary clearance position for the selected cylinder. The other cylinder may perform a predetermined piston stroke having a preset clearance position to provide a predetermined combustion, a predetermined thermal efficiency, and a predetermined exhaust gas emission. The control unit may be configured to select each cylinder according to at least one predetermined plan.

[0040] The VCR engine includes at least two cylinders, and the control unit is configured to induce piston movement for all cylinder pistons simultaneously or sequentially, having a temporary clearance position for one cylinder.

[0041] The VCR engine includes a plurality of installed cylinders, the plurality being at least three, and the control unit may be configured to induce piston movement having a temporary clearance position simultaneously for the plurality of installed cylinders. The plurality is two or more of the number of installed cylinders minus one.

[0042] Therefore, there is always a cylinder that performs a predefined piston stroke with a preset clearance position.

[0043] In an advantageous embodiment of the VCR engine, the control unit is configured to induce piston movement at the maximum compression ratio during each start and / or stop of the engine.

[0044] According to an advantageous embodiment, the VCR includes a sensor unit for detecting a value indicating the presence and / or thickness of a deposit in an area above the piston.

[0045] Deposits can cause wear steps that may lead to damage to the positioning ring.

[0046] The sensor unit may include an ultrasonic sensor. Alternatively, an optical sensor or an electromagnetic sensor for detecting resistance or capacitance may be included.

[0047] If the predetermined threshold value of the deposited amount is exceeded, purification will be required.

[0048] The control unit is configured to induce piston movement with a temporary clearance position according to the value detected by the sensor unit.

[0049] When a value corresponding to a predetermined limit for the allowable amount of deposition is detected by the sensor unit, the control unit can induce a change in the clearance position according to the plan to reduce the deposition on the inner surface of the cylinder wall.

[0050] In an advantageous embodiment, the piston is connected to a piston rod, and the piston is provided with a setting unit for controlling the compression ratio. In particular, the setting unit includes or is connected to a mechanism for displacing the normal ring of the piston relative to the piston rod. Preferably, the upper portion of the piston that wears the normal ring moves relative to the upper portion of the piston and / or piston rod.

[0051] A piston may include two or more parts that can move relative to each other.

[0052] The control unit may include or be connected to the same mechanism for displacing the normal ring of the piston relative to the piston rod or another mechanism for adjusting the temporary clearance position.

[0053] The position of the normal ring, preferably the upper part of the piston, defines the clearance position and clearance volume. The stroke length and displacement volume are maintained the same. Thus, the compression ratio can be changed by displacing the normal ring.

[0054] Alternatively or additionally, the piston is connected to the crosshead via a piston rod, and the crosshead is connected to the crankshaft via a connecting rod to drive the crankshaft.

[0055] A mechanism for controlling the compression ratio may be provided in the crosshead. In particular, the setting unit includes or is connected to a mechanism for displacing a piston rod and / or piston relative to the crosshead, as disclosed in EP2687707A2, for example.

[0056] The control unit may include or be connected to the same mechanism for displacing the piston rod and / or piston relative to the crosshead or other mechanism for adjusting the temporary clearance position.

[0057] Alternatively or additionally, the connecting rod is provided with a mechanism for controlling the compression ratio. In particular, the setting unit includes or is connected to a mechanism for displacing the connecting rod relative to the crankshaft, for example as disclosed in EP2801713 A1. This mechanism may include an eccentric tappet at the lower bearing of at least one connecting rod. The mechanism may further include a locking mechanism for locking the eccentric tappet to a corresponding crank pin of the connecting rod or crankshaft to changeably operate the reciprocating piston combustion engine at a first compression ratio or a second compression ratio, respectively.

[0058] The control unit may include or be connected to the same mechanism for displacing the connecting rod relative to the crankshaft or a mechanism for adjusting the temporary clearance position.

[0059] Alternatively or additionally, the entire piston drive unit may be moved to change the clearance position of the piston. The control unit and / or setting unit may include or be connected to a mechanism for moving the entire piston drive unit.

[0060] The present invention relates to a VCR internal combustion engine, such as a large marine or ship engine or a stationary engine, preferably having a cylinder with an inner diameter of at least 200 mm. The engine is preferably a two-stroke engine or a two-stroke crosshead engine. The engine may be a diesel or gas engine, a dual-fuel or multi-fuel engine. In such an engine, combustion of liquid and / or gaseous fuels is possible, and self-ignition or forced ignition is also possible.

[0061] The engine has at least one cylinder having a piston. The piston is connected to a crankshaft. During the operation of the engine, the piston moves between Top Dead Center (TDC) and Bottom Dead Center (BDC). The cylinder typically has at least one air passage opening for intake, specifically an air inlet located in the cylinder liner, and at least one air passage opening for exhaust, specifically an exhaust outlet located in the cylinder cover.

[0062] The internal combustion engine can be a longitudinal scavenging two-stroke engine.

[0063] The term internal combustion engine also refers to a large engine capable of operating in diesel mode (characterized by self-ignition of fuel) as well as in Otto mode (characterized by positive ignition of fuel) or a combination of these two modes. Furthermore, the term internal combustion engine specifically includes dual-fuel engines and large engines in which self-ignition of fuel is used for the positive ignition of other fuels.

[0064] The engine speed is preferably 800 RPM (4-stroke) or less, more preferably 200 RPM (2-stroke) or less, indicating a low-speed engine.

[0065] The fuel may be diesel or marine diesel oil or heavy fuel oil or emulsion or slurry or methanol or ethanol and gases such as liquid natural gas (LNG) and liquid petroleum gas (LPG).

[0066] Other possible fuels that may be added upon request include LBG (liquefied biogas), biological fuels (e.g., algae fuel or seaweed oil), hydrogen, and synthetic fuels of CO2 (e.g., made from power-to-gas or power-to-liquid).

[0067] The objective of the present invention is also achieved by a method for driving a variable compression ratio (VCR) engine comprising at least one cylinder and a movable piston configured to perform a predetermined piston stroke within the cylinder. The method comprises the steps of: setting a predetermined compression ratio by setting a predetermined clearance position; setting at least one temporary clearance position different from the predetermined clearance position; and inducing the movement of at least one piston having the temporary clearance position.

[0068] After setting the clearance position, piston motion is induced with each clearance position, each clearance volume, and each compression ratio.

[0069] During piston movement with a temporary clearance position, the inner wall of the cylinder is cleaned in the area not reached by piston movement with a preset clearance position.

[0070] Finally, the piston motion is induced again with a preset clearance position.

[0071] Preferably, piston motion having a temporary clearance position is induced according to at least one predetermined plan. The plan preferably specifies successive values ​​of the temporary clearance position, time intervals or the number of strokes for maintaining the temporary clearance position, and / or set cycles.

[0072] In particular, the plan specifies the stepwise ascent and / or descent of temporary leeway positions.

[0073] Piston movement having a temporary clearance position can be induced when necessary and / or after a predetermined number of piston strokes and / or after a predetermined operating time.

[0074] For example, at least one piston movement having a temporary clearance position can be induced every 100 to 500,000 piston strokes and / or every 1 hour to 2 months of operation time.

[0075] For a VCR engine including at least two cylinders, piston movement with a transient compression ratio can be induced for all cylinder pistons simultaneously or for a portion of the cylinders.

[0076] Advantageously, piston movement with a temporary clearance position is induced at each start and / or stop of the engine.

[0077] The clearance position can be made suitable by displacing the upper portion of the piston, including the normal ring of the piston and the normal ring, relative to the lower portion of the piston and / or piston rod.

[0078] The clearance position can be achieved by displacing the piston rod and / or piston relative to the crosshead.

[0079] The clearance position can be adjusted by displacing the connecting rod relative to the crankshaft.

[0080] In an advantageous embodiment of the present method, a value indicating the thickness of the deposit is detected, for example, by an ultrasonic sensor.

[0081] Preferably, piston movement having a temporary clearance position is induced according to the value detected by the sensor unit.

[0082] The objective of the present invention is achieved by a computer program product that can be directly loaded into the internal memory of a digital computer, and the program product includes a portion of software code for performing the steps of the method according to the above when the computer program product is executed on the computer. The plan that follows when piston movement is induced can be digitally stored in memory.

[0083] The present invention will be further described below in the form of embodiments with reference to the drawings. Brief explanation of the drawing

[0084] Figure 1 shows a schematic diagram of a first example of a combustion engine. Figure 2 shows a schematic diagram of a piston in a preset clearance position. Figure 3 shows a schematic diagram of a piston in a temporary spare position. Figure 4a shows the first typical curve of the temporary clearance position over time. Figure 4b shows the second typical curve of the temporary slack position over time. Specific details for implementing the invention

[0085] FIG. 1 shows a variable compression ratio (VCR) engine (1) including a cylinder (2), and a piston (3) is positioned to move within the cylinder (2). The piston (3) is configured to perform a predetermined piston stroke between top dead center and bottom dead center (not shown in the drawing) within the cylinder (2). In the figure, the piston (3) is shown to be in an intermediate position.

[0086] The piston (3) is connected to the crosshead (7) through the piston rod (6), and the crosshead (7) is connected to the crankshaft (8) through the connecting rod (9) to drive the crankshaft (8).

[0087] The crosshead (7) is provided with a setting unit (4) for setting a preset compression ratio. The setting unit (4) includes a mechanism for displacing the piston rod (6) and the piston (3) relative to the crosshead (7).

[0088] When the piston rod (6) is displaced relative to the crosshead (7), the range of motion of the piston (3) within the cylinder (2) changes, and the piston reaches a different normal position (not shown in the drawing) within the cylinder (2). Thus, a new preset clearance position (see FIG. 2) can be set by the control unit (4).

[0089] The VCR-engine (1) further includes a control unit (5) for setting at least one temporary clearance position (see FIG. 3) different from a preset clearance position (11) and also inducing at least one piston movement having a temporary clearance position (15).

[0090] The control unit (5) is connected to the setting unit (4). The mechanism (10) is used to adjust the preset clearance position and the temporary clearance position.

[0091] Alternatively, the control unit (5) may be connected to another mechanism (not shown in the drawing) for fitting a temporary spare position.

[0092] FIG. 2 shows a schematic diagram of a VCR engine (1) in which the piston (3) is in a preset free position (11).

[0093] The distance between the crosshead (7) and the piston (3) is set so that the piston (3) in the normal position is sufficiently below the cylinder head (12). Thus, there is a region (13) between the piston (3) and the cylinder head (12), and in this region, the inner wall (13) of the cylinder (2) is not stripped by the piston (3). In this region (13), wear steps and carbonized deposits may occur.

[0094] The VCR engine (1) may include a sensor unit (16) for detecting the thickness of the deposit, such as an ultrasonic sensor.

[0095] In the case where there is a layer of carbonized deposit thicker than a predetermined value, the control unit (5) can induce the setting of a temporary spare position.

[0096] The temporary free position can be changed to a temporary free position (15) as shown in FIG. 3, for example, by a control unit (5).

[0097] When the deposit is removed, the control unit (5) can return the free position to the original preset free position (11).

[0098] FIG. 4a shows the first typical curve of the clearance position (CP) over time (t), where the clearance position changes linearly from a preset clearance position (PCP) to a transient clearance position (TCP). FIG. 4b shows the second typical curve of the clearance position (CP) over time (t), where the clearance position changes stepwise.

[0099] Time (t) can be measured in units of time or the number of piston strokes.

[0100] The temporary free position (TCP) is the time interval (t c It can be maintained at a constant level for ).

[0101] After that, the clearance position can be lowered linearly, as shown in Fig. 4a, for example, or in steps, as shown in Fig. 4b.

[0102] The clearance position can be returned to a preset clearance position (PCP) that was maintained before the increase, or to another value as shown by the dotted line in FIG. 4a. Thus, a new preset clearance position can be selected.

[0103] The clearance position can typically vary in the range of 20 to 200 mm.

Claims

Claim 1 A variable compression ratio (VCR) engine (1), wherein the VCR engine is a large ship 2-stroke crosshead engine and comprises at least one cylinder (2), wherein a piston (3) configured to perform a predetermined piston stroke within the cylinder (2) is movably disposed within the cylinder (2), and the VCR engine also comprises a setting unit (4) for setting a predetermined compression ratio by setting a predetermined clearance position (11), and the VCR engine (1) further comprises a control unit (5) for setting at least one temporary clearance position (15) different from the predetermined clearance position (11) and for inducing at least one piston movement having the temporary clearance position (15) according to at least one predetermined plan to remove a deposit of carbon material accumulated on the inner wall of the cylinder, wherein the clearance position is changed stepwise from the predetermined clearance position to the temporary clearance position, so that the piston gradually approaches the area with the deposit, and the piston removes increasingly more deposits over the entire change curve, a variable compression ratio (VCR) engine. Claim 2 In claim 1, the plan defines at least one of a successive value of a temporary spare position (15), a time interval for maintaining the temporary spare position (15), and a setting cycle, for a variable compression ratio (VCR) engine. Claim 3 A variable compression ratio (VCR) engine according to claim 1, wherein the control unit (5) is configured to perform at least one of inducing piston movement having a temporary spare position (15) on demand, inducing piston movement having a temporary spare position (15) every 100 to 5000000 piston strokes, and inducing piston movement having a temporary spare position (15) every 1 hour to 2 months of operation time. Claim 4 A variable compression ratio (VCR) engine according to claim 1, wherein the VCR engine (2) comprises at least two cylinders (2) and the control unit (5) is configured to induce piston movement having a temporary clearance position (15) for a selected cylinder, or the VCR engine (1) comprises at least two cylinders (2) and the control unit (5) is configured to induce piston movement having a temporary clearance position (15) for one cylinder (2) simultaneously or sequentially for all cylinder pistons (3), or the VCR engine (1) comprises a plurality of installed cylinders (2), wherein the plurality is at least three, and the control unit (5) is configured to induce piston movement having a temporary clearance position (15) simultaneously for two to one number of installed cylinders (2) less than the plurality. Claim 5 In claim 1, the control unit (5) is configured to perform at least one of inducing piston movement having a temporary clearance position (15) at each start of the engine and inducing piston movement having a temporary clearance position (15) at each stop of the engine, a variable compression ratio (VCR) engine. Claim 6 In claim 1, the VCR engine (1) is a variable compression ratio (VCR) engine comprising a sensor unit (16) for detecting a value representing the thickness of a deposit. Claim 7 In claim 6, the control unit is configured to induce piston movement having a temporary clearance position (15) according to a value detected by the sensor unit (16), in a variable compression ratio (VCR) engine. Claim 8 In claim 1, the piston (3) is connected to a piston rod (6) and the piston (3) is also connected to a setting unit (4) for controlling the compression ratio, and the piston (3) includes a mechanism for displacing the normal ring of the piston (3) relative to the piston rod (6), or the piston (3) is connected to a crosshead (7) via the piston rod (6), and the crosshead (7) is connected to a crankshaft (8) via a connecting rod (9) to drive the crankshaft (8), and the crosshead (7) is connected to a setting unit (4) for controlling the compression ratio, and the crosshead (7) includes a mechanism (10) for displacing at least one of the piston rod (6) and the piston (3) relative to the crosshead (7), or the piston (3) is connected to a crosshead (7) via the piston rod (6), and the crosshead (7) is connected to a crankshaft (8) via a connecting rod (9) to drive the crankshaft (8), and the connecting rod (9) controls the compression ratio A variable compression ratio (VCR) engine connected to a setting unit (4) for control, wherein the connecting rod (9) includes a mechanism for displacing the connecting rod (9) relative to the crankshaft (8). Claim 9 In any one of claims 1 to 8, the VCR engine (1) is a large marine engine having at least one cylinder having an inner diameter of at least 200 mm, a variable compression ratio (VCR) engine.

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